Exercises: Sign / Verify Messages using Ed25519

In this exercise we shall sign and verify messages using the EdDSA digital signature algorithm and the edwards25519 curve, following the technical specification from RFC 8032. The Ed25519 digital signature algorithm can be found as library for the most programming languages.

EdDSA-Ed25519: Sign Message

Write a program to sign given text message with given private key. The input consists of 2 text lines. The first line holds the input message for signing. The second line holds the private key as hex string. Print the output as JSON document, holding the input message + the public key of the signer (as hex string, uncompressed) + the Ed25519 digital signature (as hex string).

EdDSA-Ed25519: Verify Signature

Write a program to validate the Ed25519 digital signature, created by the previous exercise. The input comes as JSON document, holding the message + the public key (uncompressed, hex string) + the signature. Print as output a single word: "valid' or "invalid".